This invention relates, in general, to a process and apparatus for converting etchants into non-hazardous material. More particularly, the present invention relates to a process and apparatus for converting cupric chloride etchant waste into non-hazardous material and for recovering copper in an oxide form from cupric chloride etchant.
One of the most critical steps in the manufacture of printed circuit boards is the etching of the unwanted copper from the substrate to form a circuit pattern. The substrate is a panel (usually 18".times.24") consisting of an insulating material made of a glass fiber weave impregnated with an epoxy resin, a paper based material impregnated with a phenolic resin, or a combination of both. This base material is then laminated to sheets of copper on one or both sides, forming the substrate from which printed circuits are made. In order to form the pattern, the substrate is coated with a photoimageable mask, commonly called dry film. New developments have resulted in the use of a "wet" photoimageable mask. A photographic pattern is placed on top of this mask and exposed to a concentrated light source. The image is then developed and the unwanted portion is washed off, leaving a hardened mask over the pattern which will form the circuit pattern desired. This mask now acts as an etch resist and the unwanted copper is removed by immersion in a cupric chloride solution. Once the copper is removed, the panel is ready for the rest of the steps involved in making a finished printed circuit board.
Once the etching baths have reached the end of their useful life, they must be treated or disposed of in a manner that eliminates the elements that make it a hazardous waste.
In batch processing, when the etchant has reached its useful life, the spent solution is pumped to a holding tank for disposition. The solution usually contains 15 to 25 ounces of copper per gallon and is classified as a hazardous waste. The current methods for disposal are to ship the spent material to a recycler or a treatment company. The material has to be manifested as a hazardous waste.
In continuous processes, an oxidizer is used to revitalize the etchant. However, in doing so, excess etchant is created which must be disposed. Etchant solutions must be disposed of in an environmentally acceptable manner.
Regeneration of the etching solution by electrowinning is a common approach along with precipitation procedures. However, electrowinning releases chlorine gas which must be captured and used in oxidizing the etchant bath. In the precipitation process, the removal of all, or a significant portion of the heavy metal content by precipitation methods as commonly used results in a sludge that is still considered a hazardous waste and is disposed of in a hazardous waste landfill.